As this kind of combustion apparatus, there is known an apparatus in patent document 1 in which, in order to improve the heat resistivity of the combustion box, water passages as a cooling means for cooling the combustion box are installed in series with the heat exchanger in that portion of the combustion box which lies between the burner and the heat exchanger. Further, in this arrangement, by interposing a packing between a combustion plate flange part on a circumference of the combustion plate and the body flange part, the sealing performance between the combustion plate flange part and the body flange part is secured.
By the way, at the time of combustion by the burner, that portion of the combustion plate flange part which faces an inner space of the combustion box will receive a considerable amount of calorific value. And when overheating of the combustion plate flange part takes place, the temperature of the burner body will reach a considerably high temperature due to transmission of heat from the combustion plate flange part. As a result, accessories of the burner body, e.g., a check valve to be disposed at a flow inlet of the burner body will be subjected to a bad effect due to heat.
Then, although not described in patent document 1, there is also conventionally known one, as shown in FIG. 7, having disposed a thermal insulation material 8 overlapping that portion of the combustion plate flange part 122 which faces the inner space of the combustion box 2. It is thus so arranged that overheating of the combustion plate flange part 122 can be prevented. In this arrangement, a fixing plate 9 for the thermal insulation material is attached to the water passages 5 disposed in that portion of the combustion box 2 which lies between the burner and the heat exchanger. By the way, in the arrangement shown in FIG. 7, there is interposed a first packing 71 between the body flange part 112 and the combustion plate flange part 122, and a second packing 72 is interposed between the combustion plate flange part 122 and the connection flange part 22. Then, in that portion of the combustion plate flange part 122 which faces the inner space of the combustion box 2, the thermal insulation material 8 is overlapped in a state in which the second packing 72 is sandwiched.
It is for the purpose of preventing the overheating of the fixing plate 9 that the fixing plate 9 for the thermal insulation material is attached to the water passages 5. However, since the water passages 5 are hollow, the fixing plate 9 will have to be attached to the water passages 5 not by spot welding but by a troublesome work of brazing. As a result, the cost for attaching the fixing plate 9 becomes expensive. Further, the thermal insulation material 8 will then be fixed to the combustion box 2 through the fixing plate 9 and the water passages 5. Therefore, when the burner has been assembled to the combustion box 2, positional deviation of the thermal insulation material relative to the combustion plate flange part 122 is likely to occur, thereby giving rise to fluctuation in the thermal insulation effect.